Nowadays, electric machines have many different uses. The use of brushless electric machines is advantageous in particular in applications in which a high level of availability and a long service life of the electric machines are important, since in these machines the brushes are not subject to any wear.
For example, such electric machines can be used in vehicles as fan motors, in order to provide air conditioning of the vehicle, for example.
Owing to faults in the electric machine or to external influences, during operation of an electric machine the rotor of the electric machine may become blocked. Such a blockage has to be detected by the actuating electronics and the power supply to the electric machine has to be interrupted in order to prevent permanent damage to the power electronics or to the electric machine.
Nowadays, there are various options for detecting a blockage of the rotor of an electric machine. In this case, it is preferable for a blockage to be detected without an additional position sensor, since this increases the system complexity and the costs.
A blockage can for example be detected on the basis of a speed of a Kalman filter used in the control of the electric machine; however, this detection is very imprecise and may therefore lead to a blockage of the rotor of an electric machine not being detected.
Alternatively, model-based methods can be used to detect a blockage of the rotor of the electric machine; however, these methods only function reliably in the upper speed range of the electric machine, since in the lower speed range of the electric machine the measurable back EMF is very low.